As an ordinary method for synthesizing a 4,4′-diformyldiphenylalkane, a method of formylation of a diphenylalkane and carbon monoxide with HF—SbF5 as a catalyst has been known (see Patent Literature 1 and Non Patent Literature 1). However, Patent Literature 1 discloses that the yield of the 4,4′-diformyl compound (which may be hereinafter referred to as a 4,4′-compound) is 98%. Non Patent Literature 1 discloses that the yield of a diformyl is 97%, but the isomer ratio of the 4,4′-compound is as low as approximately 92%.
Non Patent Literature 2 discloses that SbF5 is a viscous, colorless and transparent liquid, and has considerably strong corrosivity while it does not corrode glass.
A method of oxidation of [2.2]paracyclophane with molecular oxygen with NOBF4 (nitrosonium fluoroborate) as a catalyst in a nitromethane/dichloromethane solvent has been known (see Non Patent Literature 3). However, the use of a large amount of the chloromethane solvent, which has a large environmental load, is practically difficult, the yield is as low as 30%, and there is a problem in availability of the raw material.